Typically, wastewater influent includes ammonium nitrogen, NH4—N. Conventionally, to remove ammonium nitrogen, a two step process is called for, nitrification and denitrification. In this conventional approach to removing ammonium nitrogen, the process entails a first step which is referred to as a nitrification step and which entails converting the ammonium nitrogen to nitrate and a very small amount of nitrite, both commonly referred to as NOx. Many conventional activated sludge wastewater treatment processes accomplish nitrification in an aerobic treatment zone. In the aerobic treatment zone, the wastewater containing the ammonium nitrogen is subjected to aeration and this gives rise to a microorganism culture that effectively converts the ammonium nitrogen to NOx. Once the ammonium nitrogen has been converted to NOx, then the NOx-containing wastewater is typically transferred to an anoxic zone for the purpose of denitrification. In the denitrification treatment zone, the NOx-containing wastewater is held in a basin where there is no supplied air and this is conventionally referred to as an anoxic treatment zone. Here a different culture of microorganisms operate to use the NOx as an oxidation agent and thereby reduces the NOx to free nitrogen which escapes to the atmosphere. For a more detailed understanding and appreciation of conventional biological nitrification and denitrification one is referred to the disclosures found in U.S. Pat. Nos. 3,964,998; 4,056,465; 5,650,069; 5,137,636; and 4,874,519.
Conventional nitrification and denitrification processes have a number of drawbacks. First, conventional nitrification and denitrification processes require substantial energy in the form of oxygen generation that is required during the nitrification phase. Further, conventional nitrification and denitrification require a substantial supply of external carbon source.
In recent years, it has been discovered that deammonification can be carried out in limited circumstances in a single stage biofilm reactor. This process utilizes biofilm carriers and is designed to grow certain types of bacteria on the biofilm carriers. In particular, the targeted bacteria is aerobic ammonium oxidizing (AOB) bacteria and anaerobic ammonium oxidizing (ANAMMOX) bacteria. To a substantial extent, this approach to deammonification has been limited to sidestream applications where there is a relatively high concentration of ammonium, a relatively low concentration of organic carbon and a relatively high temperature. This process is used, for example, in treating reject water from anaerobically digested sludge. The term “reject water” means an aqueous stream that is contained within a sidestream of a wastewater treatment process and where the aqueous stream includes a relatively high ammonium concentration relative to wastewater in the mainstream.
There are many advantages to a deammonification process. Approximately 60% less oxygen is required for the removal of a certain amount of ammonium nitrogen. In addition, a deammonification process does not require an additional carbon source. Furthermore, a deammonification process results in less CO2 production and less sludge production.
Therefore, there is a need for a deammonification process that is suitable to substantially remove ammonium in both the mainstream and sidestream of a wastewater treatment process and which does not require the substantial amount of oxygen required for conventional nitrification and denitrification, and which is particularly suitable for mainstream wastewater streams that have a relatively high organic carbon content and a relatively low ammonium concentration.